We use the all-diamond tip of an atomic force microscope for the direct engraving of high-quality quantum point contacts in GaAs/AlGaAs heterostructures. The processing time is shortened by two orders of magnitude compared to standard silicon tips. Together with a reduction of the line width to below 90 nm, the depletion length of insulating lines is reduced by a factor of two with the diamond probes. The such fabricated defect-free ballistic constrictions show well-resolved conductance plateaus and the 0.7 anomaly in electronic transport measurements. © 2002 American Institute of Physics.